The projects in this Program Project proposal test the novel hypothesis that venomotor tone modulated by endothelin-1 (ET-1), partially through superoxide anion, is a contributor to the determination of systemic blood pressure. Differences in venous and arterial response to ET-1 are apparent, and these differences will be the focus of three specific aims of this project. First, veins are reported to lack ECE, a metalloprotease responsible for conversion of big ET-1 to ET-1. Second, ET-1 has a higher potency in contracting veins than arteries, and veins contract to the ETB receptor agonist sarafatoxin 6c while most arteries do not. Third, arterial vessel but not venous vessel contraction to ET is significantly reduced under conditions of hypertension. We will work with the deoxycorticosterone acetate (DOCA) salt model of hypertension as this model is ET-1 and superoxide anion-dependent. There is a significant gap in our knowledge as to ET-1 receptor pharmacology in veins, expression and processing of ET-1 in veins, and why veins remain responsive to ET-1 under conditions of normal blood pressure. The following techniques will be used to fill in these gaps and examine 3 specific aims: 1) isolated tissue bath for isometric contraction; 2) Western analyses; 3) immunohistochemistry and confocal microscopy; 4) real time RT-PCR; and 5) chemiluminescent measurement of superoxide anion. Specific Aim 1: Big ET-1 processing is different in arteries and veins, and modifies vessel responsiveness to ET receptor agonists; Specific Aim 2: ETB receptors modulate venous but not arterial tone through directly modifying contraction, altering desensitization and modifying ETA receptor function; and Specific Aim 3: Veins are more sensitive than arteries to the contractile effect of superoxide, and venous ET receptor functioning is maintained in hypertension in part by enhanced superoxide anion production. These experiments will provide information regarding ET-1 function in veins and support that venous function should be considered as a determinant of blood pressure. This work is relevant to hypertension, but also to diseases of impaired venous function such as postural hypertension, varicose veins, etc.